The present invention relates to the production of normally tacky pressure-sensitive adhesive microspheres useful in the production of removable and repositionable note paper tape and label products.
The mid-1970's saw the introduction of removable and repositionable note papers which have found broad acceptance in the marketplace. The adhesives utilized in some of the products were infusible, inherently tacky, elastomeric microspheres prepared by an aqueous suspension polymerization process. Aqueous suspension polymerization processes are described, for instance, in U.S. Pat. No. 3,691,140 to Silver, U.S Pat. No. 4,166,152 to Baker et al., U.S. Pat. No. 4,495,318 to Howard, U.S. Pat. No. 4,598,212 also to Howard, and U.S. Pat. No. 4,786,696 to Bohnel, each incorporated herein by reference.
The problem with adhesive microspheres produced by an aqueous suspension polymerization process is that there is often a need to recover the microspheres from the medium in which they are prepared, then redisperse them in a organic solvent for application to paper or another substrate. This procedure is required in the instance of paper because the presence of water will cause paper to which the adhesive microspheres are applied to curl.
It has also been stated in connection with the production of removable and repositionable products that if the adhesive force provided is too small, the product will literally fall off the surface to which it is applied, and if too great, will tear or delaminate paper surfaces at normal removal rates. Application of the adhesive coatings so as to achieve peel values within a desired range requires therefore considerable know-how.
A considerable reduction in manufacturing costs and better control over the product performance can result if the adhesive is prepared where the medium can be effectively used to control particle size and therefore adhesion and also where there can be eliminated the need to recover the adhesive from the medium in which it is prepared by a tedious and expensive step such as coagulation. This application is a continuation-in-part of application Ser. No. 07/138,509, filed 12/23/87, Now U.S. Pat. No. 4,810,763.